This specification relates to data processing.
The Internet enables access to a wide variety of resources. For example, video, audio, web pages directed to particular subject matter, news articles, images, and other resources are accessible over the Internet. The wide variety of resources that are accessible over the Internet has enabled opportunities for content distributors to provide content items with resources that are requested by users. Content items are units of content (e.g., individual files or a set of files) that are presented in/with resources (e.g., web pages). An advertisement is an example of a content item that advertisers can provide for presentation with particular resources, such as web pages and search results pages. An advertisement can be made eligible for presentation with specific resources and/or resources that are determined to match specified distribution criteria, such as distribution keywords.